1. Field of the Invention
Exemplary embodiments of the present invention relate to a multi-user multi-input multi-output (MU-MIMO) method, and an access point and a station for MU-MIMO; and, more particularly, to a MU-MIMO method in a wireless local area network (WLAN) system using multi-channel, and an access point and a station for MU-MIMO.
2. Description of Related Art
A wireless local area network (WLAN) defined in IEEE 802.11 supports a basic service set (BSS) formed of an access point and a station (STA). Lately, IEEE 802.11n was introduced. IEEE 802.11n supports a multi-input multi-output (MIMO) method for performing communication through an access point and a station which include a plurality of antennas in order to obtain high throughput (HT). The IEEE 802.22n MIMO method is a single user (SU) MIMO method where a transmitter performs a precoding operation using channel state information (CSI) for Tx beamforming (Tx BF).
In IEEE 802.11n, one frequency band channel is used for one basic service set (BBS). IEEE 802.11TGac has been developed as a follow-up standard of IEEE 802.11n. IEEE 802.11TGac requires throughput of 500 Mbps for single-access or throughput of 1 Gbps for multi-access in a MAC layer in order to support very high throughput (VHT). In order to satisfy such a requirement, IEEE 802.11 TGac was developed to support a MU-MIMO method and multi-channel.
In case of MU-MIMO, each station feeds back a channel state information matrix or a beamforming matrix to an access point. The access point performs a precoding operation using the feedback channel station information matrix (Vector) or the beamforming matrix (vector). The amount of feedback channel station information vector or beamforming vector is comparatively large. In case of using multi-channel, the amount of feedback channel station information vector or beamforming vector increases as much as the number of multi-channels because information is required to be fed back per each channel. Therefore, it has been required to develop a method for improving throughput by reducing the amount of feedback information in a WLAN system using multi-channel and MU-MIMO.